In recent years, many sunscreens and cosmetics having a sunscreening effect have been used even in daily life because the adverse influence of ultraviolet rays on the human body has been well known and because of women's desire to keep the skin white. Along with this, a class of users of sunscreens or cosmetics having a sunscreening effect have spread. These cosmetics have come to be used for not only women who are anxious about their skins but also even babies and various products are being put on the market.
An ultraviolet absorber and an ultraviolet diffusing agent are formulated in these sunscreens and cosmetic shaving a sunscreening effect to protect the skin from ultraviolet rays. Synthetic compounds are mainly used as ultraviolet absorbers and examples of these synthetic ultraviolet absorbers include benzophenones, paraaminobenzoic acids, sinnamates, salicylates, dibenzoylmethanes and benzotriazoles. The amount of these ultraviolet absorbers to be compounded in a cosmetic is regulated and it is known that these ultraviolet absorbers have safety problems such as irritation to the skin. Also, these ultraviolet absorbers differ from each other in the wavelength of ultraviolet rays at which these absorbers exhibit maximum absorption depending on their structures. It is therefore necessary that these ultraviolet absorbers are used in combinations of several types and in combination with an ultraviolet diffusing agent. Moreover, in the case of ultraviolet absorbers having poor solubility in water or oily agents, there is the case where crystals precipitate and it is therefore difficult to formulate these absorbers in cosmetics.
On the other hand, an ultraviolet protective powder, for example, inorganic pigments such as titanium dioxide and zinc oxide is used in an ultraviolet diffusing agent. These inorganic pigments are chemically or physically stable and have high safety and cut off ultraviolet rays physically, thereby making it possible to protect the skin from a wide range of ultraviolet rays. These inorganic pigments also have the effect of an ultraviolet absorber due to the absorption resulting from the bandgap transition of electrons excited from the valence electron band to the conduction band by light energy.
When the ultraviolet protective powder is formulated in a cosmetic, dust is generated and scattered in a step of dispersing the powder in a dispersion medium. Therefore, products obtained by dispersing the ultraviolet protective powder in water or oil in advance are being put on the market to protect operators from suffering from respiratory disorders, to prevent other products and working fields from being contaminated with the dust and further to improve laborsaving in the manufacturing stage and handling characteristics.
The ultraviolet protective powder is sedimented and separated in a liquid dispersion and also solidified. It is known that the stability of a dispersion is usually improved by increasing the viscosity of the dispersion and a dispersion having a solid clay form obtained by excessively increasing the viscosity based on this fact is also being put on the market. However, such a dispersion having a solid clay form poses the handling problem that it is handled with difficulty when it is formulated in a cosmetic and it has poor dispersibility in a cosmetic.
Also, these dispersions have the problem that dispersion stability is deteriorated at lower temperatures or higher temperatures or along with a variation in temperature because the ultraviolet protective powder is different from the dispersion medium in thermal expansion coefficient and shrinkage factor.
As the method of dispersing the ultraviolet powder, a method of adding a dispersant is usually used. Examples of the dispersant include, besides a dispersion solution comprising using a glucose fatty acid ester having an acyl group having 10 to 14 carbon atoms (see Patent document 1), dispersants such as diglyceril monoisostearate, diglyceryl diisostearate, glyceryl monoisostearate, polyoxyethyleneglyceryl isostearate having a HLB of 8 or less, polyoxyethylene glycol isostearate having a HLB of 8 or less, dextrin fatty acid ester, crosslinking type methylpolysiloxane, cellulose, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, polyhydroxystearic acid, polyhydroxycarboxylic acid, ethoxylated phosphate and reactive organic silicone (see, for example, Patent documents 2, 3 and 4).
Also, a pigment dispersion is disclosed which comprises a dispersant mixture containing an ester oil, an alkyl and/or alkenyl oligoglucoside and polyol poly-12-hydroxystearate (see, for example, Patent document 5).
As a method using no dispersant, there is a method in which the surface treatment of a microparticle ultraviolet protective powder is specified (see Patent document 6).
Patent document 1: Publication of JP-A No. 3-15463.1
Patent document 2: Publication of JP-B No. 6-61457
Patent document 3: Publication of JP-A No. 2001-58935
Patent document 4: Publication of JP-A No. 2002-80771
Patent document 5: Publication of Japanese Patent Application National Publication (Laid-open) No. 2001-524504
Patent document 6: Publication of JP-A No. 2002-80748
Patent document 1 relates to a solvent type or water-type pigment dispersion, which is, however, limited in use for w/c type sunscreening cosmetics that are main current and have high water resistance.
Also, in Patent documents 2 to 4, a dispersant is used to thereby improve the dispersibility of microparticle ultraviolet protective powder in oil and the like. However, in these references, the powder is inferior in dispersing stability at high temperatures or low temperatures or when the temperature is varied or when it is stored for a long time. Also, there is the case where coagulation arises and the emulsion is made unstable when the powder is formulated in a cosmetic, and finally, only insufficient dispersibility is obtained, so that a desired ultraviolet protective effect is not obtained.
Also, in Patent document 5, the amount of the ultraviolet protective powder to be compounded is as small as 0.1% to 5%, which is a concentration not enough to produce a sunscreen having a high ultraviolet protective effect by only the inorganic ultraviolet protective powder. In Patent document 6, problems, for example, the occurrence of coagulation when the powder is dispersed in an oil agent still remains though this depends on the formulation.
Accordingly, the present invention relates to an ultraviolet protective preparation which allows ultraviolet protective powder such as titanium dioxide and zinc oxide to disperse stably in an ultraviolet protective preparation and is superior in handling characteristics and dispersibility in a cosmetic and also relates to an ultraviolet protective preparation-containing cosmetic having a high function and storage stability.